Apparatus for web drying



W. ROSENBAUM APPARATUS FOR WEB DRYING Filed July 6, 1955 4 Sheets-Sheet 1 INVENTOR. WEEK/E2 EQSEIVBAUM y 1957 w. ROSENBAUM 2,791,039

APPARATUS FOR WEB DRYING Filed July 6, 1955 4 Sheets-Sheet 2 INVEN TOR.

(/4 (/2 met/v52 mam/54am WWW May 7, 1957 Filed July 6, 1955 W. ROSENBAUM APPARATUS FOR WEB DRYING 4 Shee'ts-Sheetf IN VEN TOR. WECA/EZ ZOSEA/BAU/W United States Patent APPARATUS non WEB DRYING Werner Rosenbaum, New York, N. Y., assignor to ChamplainCompany, Inc., Bloomfield, N. 1., a corporation of New York Application July 6, 1955, Serial No. 520,285

19 Claims. (Cl. 34-160) This invention relates to web drying in general, and more particularly to apparatus for drying a rotogravure printed web.

Rotogravure printing presses are used with inks having a volatile solvent, and the printed web is passed through driers, in order to make possible high printing speed; This is particularly true when doing multi-color work in which the web passes through successive printing units. A favored type of drier is in the form of an inverted U disposed over each unit of the printing press, so that the line of presses may be disposed in compact succession. Such an arrangement is disclosed in U. S. Patent'2,554,- 239, issued on May 22, 1951, to Joseph R. Caulfield and Milton E. Hanson.

However, there are many other uses in industry for a drier which will rapidly dry a fast moving web, and the present invention, when considered in certain aspects, is not limited to rotogravure printing.

The usual drier blows heated air against the web. A common method of heating the air is to pass the same through steam coils located within the top of the hood of the drier, the steam being generated in a remote boiler and piped to the driers. The steam pressure is kept below fifteen pounds per square inch because a higher pressure requires the useof a licensed stationary engineer. This in turn limits the steam to a temperature of, say, 250 F. and after heat exchange this gives the air a temperature of only, say, 200 F.

Another method of heating air is to pass the same over electric elements, but this is not economical because of the high cost of electric energy in most places. More'- over, if temperatures above, say 300 F. are to be used, the electric heating elements themselves become costly.

It has also been suggestedto pass air over an open flame, but the heater then must be kept a considerable distance away from the web because of the volatile sol vents or vapor thereat. This requires an expensive and bulky installation, and it also requires many expensive controls for automatically taking care of purging and flame failure, etc.

The primary'obje'ct of the present invention is topro; vide a drier which produces and utilizes unusually high temperature air for rapid drying of a web, thus making possible higher web speeds, particularly in rotogravure printing. A further object is to provide such a drier which may be localized immediately at the printing press without loss of safety. Indeed the present drier is substantially the same in appearance and compactness as steam driers heretofore employed, yet operates at a much higher temperature, and Without contact of solvent-laden air with the high temperature heating unit.

Still another object is to employ a radiant heating tube the inside of which is flame heated, as by means of a fluid fuel burner, typically a gas burner, the said radiant heating tube being located within the hood'of the drier, thus dispensing with the need for an outside steam boiler.- Further objects are to provide for partial recirculation of the used air, and partial replacement by freshly heated 2391,0 39 Patented May 7, 1957 air; to pass the fresh air out not the recirculated air over the radiant tube; to provide separate fans for recirculation and for heating; and to provide a pressure differential which itself insures against contact of the reused or vaporladen air with the radiant heater tube.

To accomplish the foregoing general objects, and other more specific objects which will hereinafter appear, my invention resides in the drier elements, and their relation one to another, as are more particularly described in the following specification. The specification is accompanied by drawings, in which:

Fig. l is a vertical section through a drier embodying features of my invention, the said section being taken longitudinally of the web;

Fig. 2 is a vertical section taken transversely of the web and approximately in the plane of the line 2-2 of Fig. 1;

Fig. 3 is a horizontal section taken approximately in the plane of the line 3-3 of Fig. 1;

Fig. 4 is a horizontal view of a partition disposed between the fresh air heating fan and the recirculation fan;

Fig. 5 is an end elevation of said partition;

Fig. 6 is a front elevation of said partition;

Fig. 7 is a horizontal section below the aforesaid partition to show a baffie wall which acts as an inlet for the recirculating fan;

Fig. 8 is an end elevation of the baflle wall;

Fig. 9 is a front elevation of the bathe wall;

Fig. 10 is a view similar to Figs. 5 and 8, but showing the partition and battle wall in assembled relation; and

Fig. 11 is an elevation of a multi-color printing press, drawn to small scale, and showing the location of the driers.

Referring to the drawing, and more particularly to Fig. 11, the multi-color printing press there shown cornprises a reel carrier generally designated 12, and a power driven web feed unit generally designated 14. The web is then fed through successive printing presses 16, 18, 20 and 22, having individual driers or hoods associated therewith, as indicated at 26, 28, 30 and 32, respectively. The web leaving the last drier is rewound by a suitable rewind unit 34. Although not shown in detail, it will be understood that the reel carrier 12 is arranged to support two reels 36 and 38, for rapid change'from an exhausted reel, and for splicing to the web of a new one. The web feed unit 14 and the rewind unit 34 each may be provided with independent variable speed drives, with appropriate mechanism to maintain constant web tension. The assembly of multi-color presses is driven by a main drive motor and a common shaft, with appropriate intermediate mechanism at each press for adjusting the registration of the printing.

The web is printed while passing between a gravure cylinder 40 and a pressure roll 42. The additional rolls shown provide an inverted U-shaped web lead immediately after the printing operation, with the printed surface on the outside, so that it is exposed to the inverted U-shaped drier immediately around the web.

The drier arrangement is shown in greater detail in Figs. 1, 2 and 3, referring to which the drier comprises a radiant tube 44, a burner 46 (Fig. 3') for flame heating theinside of the tube, a plenum chamber (48, 50, 52 in Fig. 1) disposed immediately adjacent the web 54 for directing heated air against the web, and means 56 for blowing air over the radiant tube 44 and thence to the plenum chamber. A nozzle plate (58, 60 and 62 in Fig. l) is preferably disposed between the plenum chamber and the Web, in order to better direct the heated air from the chamber against the web.

The guide rollers 64 and 66 may be idle rollers which are mounted on and effectively form a part of the printing press, ,their purpose being to guide the web in inice verted U form at each unit of the press, as shown by the broken line 54, for cooperation with the drier. In the form here shown there are two upright nozzle plates 58 and 62, and a horizontal nozzle plate 60, and the plenum chamber may be considered to comprise two upright plenum chambers 48 and 52, connected by a horizontal plenum chamber 50'.

As so far described it would be necessary to heat new air in excessive quantity, but in practice a considerable part of the heated air is recirculated and reused, and only a fraction of the air is exhausted or discharged to suitable recovery apparatus for extraction of the solvent carried thereby. More specifically, in Figs. 1 and 2 it will be seen that there are two fans 56 and 70. The fan 70 serves to recirculate used air leaving the web back to the. plenum chambers and nozzle plates for reuse. The fan 56 receives fresh air and blows the same past the radiant tube 44 to the plenum chambers. In accordance with an important feature of the present invention, the fan 56 has a discharge pressure higher than that of the fan 70 and thereby serves not only to displace a part of the used air, but with the aid of appropriate partition and bafile walls to separate the action of the two fans, serves to prevent used air from reaching or passing over the radiant heater tube, and thus guards against possible ignition or explosion of the solvent vapors. The fans 56 and 70 are preferably carried in superposed relation on a single vertical shaft and may be driven by a single motor, thus guarding against the possibility of one fan operating while the other may be stopped.

Considering the arrangement in greater detail, and referring to Fig. 3, the tube 44 is disposed in a generally horizontal plane within the top of the hood of the drier, and isshaped to form a nearly closed figure. In the present case this is a square with four sides 72, 74, 76 and 78. The tube is made of a suitable alloy steel, and the'co'rners may be mitred and welded to provide the sharp angles shown. A corner piece 80 may be welded inside the first bend, as shown, in order to help deflect the long flame from the burner 46. The burner may be conventional, and in the present case is a No. 630-P burner manufactured by I-Iauck Manufacturing Co. of Brooklyn, New York. This burner is arranged for a gas connection at 82, an air connection at 84, and electrical connections at 86 for ignition. The burner will operate with either fuel oil or gas, but for the present purpose'it is assumed that gas is being used, as would be preferred in most printing plants. 7

In the leg 78 of the radiant tube a mixing means may be provided, as by the use of vertical and horizontal tubes 88 and 90 disposed diametrically of the radiant tube 78 and intended to insure a final mixing and combustion of gases before reaching the sloping flue connection 92. In Fig. 11 it will be seen how these sloping flue connections may lead to a common flue 94, which in turn is connected to a stack 96. It will be understood that the term stack is employed for convenience, and that his not necessary to have a true stack in the sense of providing height and draft, it being sufficient to discharge the combustion gases in a safe location.

In Fig. 3 it will be seen that the fan 56 is of the centrifugal type, and that it is located within the nearly closed figure formed by the radiant tube. To help insure'distribution of the air blown outward, a number of stationary distribution vanes 100 may be provided, these being located outside the fan rotor. The latter may be conventional, it having blades 102 mounted between a bottom disc 104 and a'top disc 106, the latter being annular or having a center opening 188- which acts as a fresh air inlet, the air coming in from above, as is best shown in Figs. 1 and 2. Only half the blades are shown.

In Fig. 1 it will be seen'that there is a generally horizontal partition 110 disposed between the lower fan 70 and the upper fan 56. The partition comprises not only the flat plate portion 110 but also a frusto-conical'portion 112, the upper edge of which is disposed immediately below the fan 56. Thus the partition separates the action of the two fans.

Referring now to Figs. 4, 5 and 6 of the drawing, I there show the flat partition with its frusto-conical portion 112. The ends of partition 110 are cut away to provide passes 114 and 116. These are disposed over the upright plenum chambers 48 and 52, as will be seen in Fig. 1, and thus feed newly heated fresh air downward to the plenum chambers 48 and 52.

Reverting to Figs. 4, 5 and 6, there are two additional passages 118 and 120 cut through the partition 110. These lead directly to rectangular ducts 122 and 124. The said ducts are more clearly shown in Fig. 7, which is a horizontal view taken below the partition 110.

Referring next to Fig. 2 of the drawing, the ducts 122 and 124 lead to the horizontal plenum chamber 50, and thus newly heated fresh air is supplied to that plenum chamber (along with recirculated air leaving the lower fan 70) as well as to the upright plenum chambers as previously mentioned.

The web has a width corresponding to the plenum chamber 50 (Fig. 2) and its horizontal nozzle plate 60. The upright nozzle plates 58 and 62 (Fig. 1) have the ,same width, and the nozzles may be in the form of horizontal slots of appropriate cross-section, these slots being indicated at 59 in Fig. 2. The arrangement of nozzle plates and plenum chambers in inverted U-shape probably requires no detailed description, it being disclosed in the aforesaid Caulfield and Hanson Patent 2,554,239. The complete drier housing is substantially wider than the web, thereby providing return passages at 126 (Fig. 2). It will be understood that there are four such return passages in all, at the four corners or legs of the drier. These are connected at their upper ends by horizontal return passages 128, and an exhaust duct 130 (Fig. 2) may be connected at any convenient point to one of the horizontal return passages 128. These exhaust ducts for each of the driers may be connected to a common exhaust duct one end of which is indicated at 132 in Fig. 11, and the duct 132 may lead to the atmosphere if no solvent recovery is wanted, or, as is more usually the case, the duct 132 leads to appropriate solvent recovery apparatus.

, Duct 132 may be provided with a suction fan, not shown. This supplements the positive pressure developed by the upper fan 56, which may be a matter of, say, seven inches of water. The lower fan 70 has a lower discharge pressure than the upper fan 56, and the ratio of new air to recirculated air depends on this difference in pressure, but may be addition-ally controlled or modi fied by appropriate dampers in the exhaust duct system. Individual dampers for each drier are preferred. The vertical Walls 129 (Fig. 2) above nozzle plate 60 insure that the air leaving through the exhaust duct 130 will be solvent-laden or used air, rather than newly heated fresh air coming down from above. The dampers may be in connections 130.

Referring now to Figs. 1 and 7 of the drawing, another partition or baffle plate 134 is disposed beneath the partition 110. At their outer edges these are joined by upright walls 136. The baffle 134 slopes at its end portions as shown, but is preferably horizontal in its middle portion as indicated at 138, and this middle portion has a circular opening surmounted by a frusto-conical bathe 140.

Fan 70 is a centrifugal fan generally like fan 56, and has a bottom plate 142 (Fig. 1) and an annular top plate 144, with appropriate spiral or radial blade-3 therebetween (not shown). The opening within top annulus 144 acts as an air inlet, and in accordance with my invention the annulus 144 is supplemented by a reversely bent inlet 146 the peripheral edge of which overlies theinner edge of the frusto cone 140. The trapezoidally shaped spaces defined between partition 1-10 at the top, the baflie 134 at the bottom, and upright walls 136, are open at their ends to receive the used or returned air leaving the web and flowing upward from the four corners of the drier and from the sides of the drier. This air cannot flow upward through the passages 114 and 116 because the fan 56 is blowing downward. It cannot reach the inlet of the upper fan 56 because that is open only at the top and solely to the outside or room air. It can flow, however, directly to the inlet of the lower fan 70, and indeed is both pushed and drawn there through the trapezoidal spaces here shown.

Referring to Figs. 7, and 9, the bafiie 134, 138 with its frusto cone 140 extends generally in the direction of web travel (from right to left as shown) and is narrower than the drier and the partition 110 shown in Fig. 4. Thus the ends of the trapezoidal passages are directly open to the return legs 126 and the corresponding legs at the other two corners, as well as to the horizontal connecting passages 128 at the tops of the legs.

The manner in which the partition 110 and the bafile 134 come together is illustrated in Fig. 10, which essentially is merely a combination of Figs. 5 and 8. The upper and lower members are connected by the rectangular ducts 122 and 124, and are also connected by the upright end walls 136, which have been omitted in Fig. 8, but are shown in Fig. (and also in Figs. 4-7).

Reverting to Fig. 1, the heat transfer area of the raidiant tube may be increased by the use of fins or the like, but in the present case is increased in simpler fashion by the provision of a metal wire mesh screen 150, which may be folded about a rod 152 secured to partition 110, and which has its upper or free edges secured to the drier at 154. The metal screen is so positioned that it bears against, and indeed preferably is bent around the radiant tube, thus insuring good heat conductive contact therebetween. Inasmuch as the screen extends entirely across the path of air leaving the fan 56, all of the air must come in contact with the screen, and the latter assumes a temperature-nearly as high as that of the tube.

The temperature which may be employed in this apparatus is in marked contrast with the comparatively low temperature available in a steam system. The radiant tube may be brought to a temperature of 1800 F. at its surface. The air is easily heated to a temperature of 500 F. and could be heated to a higher temperature of, say, 600 or 700 F. if desired. With these high temperatures the drier is preferably heat insulated, and thus comprises not only a metal shell or hood indicated at 156 (Fig. l), but also a heat insulating and preferably refractory lining 158.

As in the Caulfield and Hanson Patent 2,554,239 previously referred to, the leg portions" of the drier are preferably hinged at 160 so that they may be turned upwardly and outwardly. The upright nozzle plates 58 and 62" form a part of the legs, and also move out of the way at this time, thus facilitating webbing the press. The side wall above the legs (161 in Fig. 11) of the drier, on one side, is hinged at the top to turn upward out of the way, thus exposing the guide rollers 64 and 66 (Fig. 1) to facilitate threading the web through the press.

The bottom fan 70 is smaller in diameter than the superposed frusto cones 140 and 112. When the top plate of the drier is removed the complete fan assembly may be raised out of the drier by pulling the same vertically upward. It is primarily for this reason that the special inlet ring 146 is employed and is made rotatable, that is, it is secure to and becomes a part of the lower fan rotor, so that it comes up with the fan assembly instead of blocking removal of the same. The burner may be serviced without removing the radiant tube, for it is simply pulled longitudinally out of the end of the radiant tube. When the top of the drier is removed the entire radiant heater tube may be lifted upward out of the drier for servicing without disturbing the wire mesh screen, which simply remains in position until the radiant tube assembly is returned.

The fan rotors are both mounted on a common shaft 162, and this is driven by one or more pulleys 164. The driving motor is indicated at 166, and carries pulleys 168. Conventional V belts are used between the pulleys 168 and 164. Shaft 162 turns in bearings 170 carried by a bearing plate 172 which is supported by a suitable bracket assembly 174 (Fig. 2). The mounting of the bearing plate and bracket assembly is by means of removable bolts (not shown) which are released before attempting to raise the fan assembly out of the drier for servicing or the like.

One important advantage of the present drier is the isolation of the solvent-laden air from the radiant heating tube. This makes it possible to locate the latter not only close to but within the drier, and despite the fact that the temperature of the radiant tube may be much higher than the autogenous ignition temperature of the solvents used in the rotogravure inks. Because of this safety feature it is not necessary to provide the drier with complex and expensive automatic purging equipment and flame failure equipment. Indeed it may be mentioned that the radiant tube is sturdy and capable of withstanding considerable pressure, and that fact, together with the absence of any significant obstructions in the radiant tube itself, makes it possible for the tube to readily withstand the force of any minor backfire or explosion at the burner itself.

It is believed that the construction and method of use, as well as the advantages of my improved indirect flame heated hot air drier, will be apparent from the foregoing detailed description thereof. Air temperatures may be used much higher than those feasible with steam heat, thus making possible higher web speeds. Heat is generated economically with a commonly available fluid fuel, and the drier is completely self-contained. The economy of recirculation of heated air is retained, without danger of bringing solvent-laden air into contact with the radiant tube. Electronic controls for purging and flame failure are unnecessary. The complete drier is of the same general configuration and size as those already in common use in multi-color gravure printing presses. The radiant tube and the burner used therewith may be conventional, thus taking advantage of improvements made in recent years for other purposes. The heat transfer surface is increased, and heating of all of the air is assured, in an economical manner by the use of metal wire mesh. Dual high and low pressure fans mounted on a common shaft may be employed for recirculation and for the addition of fresh air.

It will be understood that while I have shown and described my invention in a preferred form, changes may be made in the structure shown, without departing from the scope of the invention, as sought to be defined in the following claims. In the claims the reference to the radiant tube being a nearly closed figure is not intended to exclude a U shape having three of the four sides shown, or a tube bent to rounded instead of mitred shape.

I claim:

1. A drier for a moving printed Web, said drier comprising a heater chamber, a radiant tube in said heater chamber, a burner for projecting flame inside said tube, a plenum chamber disposed immediately adjacent the web for directing heated air against the web, said chambers servnig to shield the web from said radiant tube, and means for blowing air over said radiant tube to said plenum chamber.

2. A drier for a moving printed web, said drier comprising a heater chamber, a radiant tube in said heater chamber, a fluid fuel burner in one end of said tube to flame heat the inside of said tube, the other end'of said tube being connected to a suitable stack, a plenum chamber disposed immediately adjacent the web, said chambers serving to shield the web from said radiant tube, ,a nozzle plate between said plenum chamber and said web for directing heated air from the chamber against the web, and a fan for blowing air over the outside of said radiant tube to said plenum chamber.

3. A drier for aimoving printed web, said drier being in the shape of an inverted U, there being upright and horizontal nozzle plates immediately around the web and plenum chambers outside said nozzle plates, a heater chamber at the top of said drier, a radiant tube disposed in a generally horizontal plane in said heater chamber at the top of the drier and shaped to form a nearly closed figure, said chambers serving to shield the web from said radiant tube, a burner, to flame heat the inside of said tube, and a fan disposed at said nearly closed figure for blowing air outwardly over said tube and thence downwardly to the plenum chamber of the drier.

4.. A drier for a rotogravure printing press, said drier being in the shape of an inverted, U mounted over the printing press, there being upright and horizontal nozzle plates immediately around the web and plenum chambers outside said nozzle plates, a heater chamber at the top of said drier, a radiant tube disposed in a generally horizontal plane in said heater chamber at the top of the drier and shaped tov form a nearly closed figure, said chambers serving to shield the web from said radiant tube, a fluid fuel burner, inserted in the entrant end of said tube, the exit end of said tube being connected to a stack, a fan of the centrifugal type mounted on an upright shaft and disposed within said nearly closed figure for blowing air outwardly over said tube and thence downwardly to the plenum chambers of the drier.

5. A drier for a moving printed web, said drier comprising a heater chamber, a radiant tube in said heater chamber, a fluid fuel burner in one end of said tube to flame heat the inside of the tube, the other end of said tube being connected to a suitable stack, a plenum chamber disposed immediately adjacent the web, said chambers serving to shield the web from said radiant tube, a nozzle plate between said plenum chamber and said web for directing heated air from the chamber against the web, a first fan for receiving air leaving said web and recirculating the same to the plenum chamber through the nozzles to the web, and a second fan for receiving fresh air and blowing the same over the radiant tube to the plenum chamber, said second fan being designed to discharge air ata pressure somewhat higher than that of the air discharged by the first fan, whereby a desired portion of the recirculated air is displaced by fresh air.

' 6. A drier for a moving printed web, said drier comprising a heater chamber, a radiant tube in said heater chamber, a burner for projecting flame inside said tube, a plenum chamber disposed immediately adjacent the web for directing heated air against the web, said chambers serving to shield the web from said radiant tube, a first fan for receiving air leaving said web and recirculating the same to the plenum chamber, and a second fan for receiving fresh air and blowing the same over the radiant tube to the plenum chamber, said second fan being designed to discharge air at a pressure somewhat higher than that of the air discharged by the first fan, whereby a desired portion of the recirculated air is displaced by 'fresh air. 1 V g i 7. A drier for a moving printed Web, said drier being in the shape of an inverted U, there being upright and horizontal nozzle plates immediately around the web and plenum chambers outside said nozzle plates, a heater chamber at the top of said drier, a radiant tube disposed in a generally horizontal plane in said heater chamber at the top of the drier and shaped to form a nearlyclosed figure, said chambers serving to shield the web from said radiant tube, a burner to flame heat the inside of said tube, two fans, one fan serving to recirculate used air leaving the web back to the plenum chambers and nozzle 8 plates for reuse, the second fan receiving fresh air and blowing the same past the tube to the plenum chambers, the second fan having a discharge pressure higher than thatof the first fan in order to displace a portion of the used air, there being appropriate partition and baflle walls to separate the action of the two fans and to prevent used air from passing over the radiant heater tube.

8. A drier for a moving printed web, said drier being in the shape of an inverted U, there being upright and horizontal nozzle plates immediately around the web and plenum chambers outside said nozzle plates, a heater chamber at the top of said drier, a radiant tube disposed in a generally horizontal plane in said heater chamber at the top of the drier and shaped to form a nearly closed figure, said chambers serving to shield the web from said radiant tube, a burner to flame heat the inside of said tube, two superposed fans of the centrifugal type mounted on a single vertical shaft, the lower fan serving to recirculate used air leaving the web back to the plenum chambers and nozzle plates for reuse, the upper fan being disposed at the aforesaid nearly closed figure for receiving fresh air and blowing the same past the tube to the plenum chambers, an exhaust duct connected to said plenum chambers for discharge of a portion of vaporladen air, the upper fan having a discharge pressure higher than that of the lower fan in order to displace the aforesaid portion of the vapor-laden air to the exhaust duct, there being appropriate partition and baflle walls to separate the action of the two fans and to prevent vaporladen air from passing over the radiant heater tube.

9. A drier for a rotogravure printing press, said drier being in the shape of an inverted U mounted over the I printing press, there being upright and horizontal nozzle plates immediately around the web and plenum chambers outside said nozzle plates, a heater chamber at the top of said drier, a radiant tube disposed in a generally horizontal plane in said heater chamber at the top of the drier and shaped to form a nearly closed figure, said chambers serving to shield the web from said radiant tube, a fluid fuel burner inserted in the entrant end of said tube, the exit end of said tube being connected to a stack, two fans, one fan serving to recirculate used air leaving the web back to the plenum chambers and nozzle plates for reuse, the second fan receiving fresh air and blowing the same outwardly past the tube to the plenum chambers, an exhaust duct connected to said plenum chambers for discharge of a portion of vapor-laden air, the second fan having a discharge pressure higher than that of the first fan in order to displace the aforesaid portion of the vaporladen air to the exhaust duct, there being appropriate partition and baffle walls to separate the action of the two fans and to prevent vapor-laden air from passing over the radiant heater tube.

10. A drier for a rotogravure printing press, said drier being in the shape of an inverted U mounted over the printing press, there being upright and horizontal nozzle plates immediately around the web and plenum chambers outside said nozzle plates, a heater chamber at the top of said drier, a radiant tube disposed in a generally horizontal plane in said heater chamber at the top of the drier and shaped to form a nearly closed figure, said chambers serving to shield the web from said radiant tube, a fluid fuel burner inserted in the entrant end of said tube, the exit end of said tube being connected to a stack, two superposed fans of the centrifugal type mounted on a single vertical shaft, the lower fan serving to recirculate used air leaving the web back to the plenum chambers and nozzle plates for reuse, the upper fan being disposed within the aforesaid nearly closed figure for receiving fresh air and blowing the same outwardly past the tube to the plenum chambers, an exhaust duct connected to said plenum chambers for discharge of a portion of vaporladen air, the upper fan having a discharge pressure higher than that of the lower fan in order to displace the aforesaid portion of the vapor-laden air to the exhaust duct.

there being appropriate partition and baffle walls to separate the action of the two fans and to prevent vapor-laden air from passing over the radiant heater tube.

11. A drier as defined in claim 1, in which the effective heat transfer surface area of the radiant tube is increased by a wire mesh screen disposed across the flow path of the air blown across the tube, said tube being in close contact with the radiant tube.

12. A drier as defined in claim 3, in which the effective heat transfer surface area of the radiant tube is increased by a wire mesh screen disposed across the flow path of the air blown across the tube, said tube being in close contact with the radiant tube.

13. A drier as defined in claim 5, in which the eifective heat transfer surface area of the radiant tube is increased by a wire mesh screen disposed across the flow path of the air blown across the tube, said tube being in close contact with the radiant tube.

14. A drier as defined in claim 7, in which the effective heat transfer surface area of the radiant tube is increased by a wire mesh screen disposed across the flow path of the air blown across the tube, said tube being in close contact with the radiant tube.

15. A drier as defined in claim 9, in which the effective heat transfer surface area of the radiant tube is increased by a wire mesh screen disposed across the flow path of the air blown across the tube, said tube being in close contact with the radiant tube.

16. A drier as defined in claim 7, in which the fans are superposed on a common vertical shaft, and in which the entire periphery of each of the fans is open for discharge of air in all directions, and in which a partition is disposed between the upper and lower fans, said partition being cut away at its ends over the upright plenum chambers for supply of fresh heated air to said chambers, said partition further having upright ducts leading to the horizontal plenum chamber, said lower fan discharging into said upright and horizontal plenum chambers, and additional walls for guiding used air from the web back to the inlet of the lower fan and below the aforesaid partition for recirculation, without contact with the radiant heater tube.

17. A drier as defined in claim 9, in which the fans are superposed on a common vertical shaft, and in which the 10 entire periphery of each of the fans is open for discharge of air in all directions, and in which a partition is disposed between the upper and lower fans, said partition being cut away at its ends over the upright plenum cham bers for supply of fresh heated air to said chambers, said partition further having upright ducts leading to the horizontal plenum chamber, said lower fan discharging into said upright and horizontal plenum chambers, and additional walls for guiding used air from the web back to the inlet of the lower fan and below the aforesaid partition for recirculation, without contact with the radiant heater tube.

18. A drier as defined in claim 8, in which a generally horizontal partition is disposed between the upper and lower fans, said partition being cut away at its ends over the upright plenum chambers for supply of fresh heated air to said chambers, said partition further having upright ducts leading to the horizontal plenum chamber, said lower fan discharging into said upright and horizontal plenum chambers, and additional walls for guiding used air from the web back to the inlet of the lower fan and below the aforesaid partition for recirculation, without contact with the radiant heater tube.

19. A drier as defined in claim 10, in which a generally horizontal partition is disposed between the upper and lower fans, said partition being cut away at its ends Over the upright plenum chambers for supply 'of fresh heated air to said chambers, said partition further having upright ducts leading to the horizontal plenum chamber, said lower fan discharging into said upright and horizontal plenum chambers, and additional walls for guiding used air from the web back to the inlet of the lower fan and below the aforesaid partition for recirculation, without contact with the radiant heater tube.

References Cited in the file of this patent UNITED STATES PATENTS 1,858,714 Martin May 17, 1932 2,091,172 Wilson Q. Aug. 24, 1937 2,249,411 Woodson July 15, 1941 2,471,802 Walter et a1. May 31, 1949 2,554,239 Caulfield et a1. May 22, 1951 2,558,338 Clements June 26, 1951 2,724,907 Walter Nov. 29, 1955 

